The present invention relates to a magnetic recording and reproducing apparatus, and more particularly to a rotating magnetic head (hereinbelow, simply termed "rotating head") device which is well suited to reduce the size of the apparatus and to stabilize the traveling of a tape and prevent the damage of the tape.
The present invention further relates to a rotating head device, and more particularly to a rotating head device which has built-in large-sized rotary transformers coping with the multi-channeling of signals and which is well suited for a smaller size owing to the reduction of the diameters of cylinders.
At the present time, there are high needs for reduction in the sizes of video tape recorders (VTR's), and various measures for reducing the sizes of mechanisms have been proposed. With any of the methods, however, the geometries of the entire mechanism are substantially determined by the sizes of a cassette and a rotating head device.
In this regard, an example which pursues the utmost limits of the size of the mechanism for system specifications such as the shapes of the cassette and the rotating head device is as disclosed in the official gazette of Japanese Patent Application Laid-open No. 171070/1984. This measure consists in that, as shown in FIG. 1 of the drawings annexed herewith, a ring 106 of the rotating head device is pressed into and caused to overlap the front opening 104 of the cassette 102, thereby to reduce the depth of an apparatus. Such a measure is effective for a system, for example, the VTR of 8 mm-FORMAT in which the opening of the cassette is large. In the figure, numeral 101 designates a tape guide drum, and numeral 103 designates tape part, respectively.
The prior art, however, has the following problems (1), (2), (3) and (4), which are more serious especially in a system of so-called wide-angle winding wherein a tape is wound round a rotating head over an angular extent of at least 180.degree.:
(1) In order to insert the rotating head device into the opening of the cassette, this rotating head device needs to be arranged at a low position while avoiding the inner lid and top case of the cassette. This increases the height of the whole apparatus, and forms a factor obstructive of the thinning of the apparatus.
(2) For the purpose of arranging the rotating head device which is basically cylindrical, at the highest possible position within the cassette opening, preferably the angle of inclination of the rotating head device with respect to a chassis is made small so as to flatten the top surface of the rotating head device. Since, however, a tape is wound obliquely to the rotating head device, the heights of the tape parts obliquely traveling on the entrance side and exit side of the rotating head device become different. Accordingly, the traveling path of the tape becomes a multilevel one, and in particular, the tape lowers on the exit side, so that the whole apparatus thickens.
(3) In executing multilevel tape loadings on both the sides of the rotating head device, a loading mechanism becomes complicated, and this hampers reducing the size and lightening the weight of the apparatus.
(4) In the aforementioned case where the angle of winding of the tape round the rotating head is large, there is a place in which the traveling direction of the tape changes acutely, and hence, the smooth traveling performance of the tape is liable to degrade.
As disclosed in the official gazette of Japanese Patent Application Laid-open No. 150125/1980, another prior-art example has pursued the thinning of a rotating head device alone and therefore has a structure wherein electromagnetic components such as brushless motor parts, frequency generator (FG) parts and a rotary transformer are distributively arranged above and below the rotating plane of magnetic heads, namely, an arrangement wherein at least the rotary transformer and the brushless motor are distributed above and below a rotating drum on which the magnetic heads are mounted.
A tape cassette and the rotating head device combined with each other cannot be skillfully caused to overlap on account of the protrusion of, e. g., the lid of the tape cassette which is opened for drawing out a magnetic tape, so the combination hampers reduction in the horizontal area of the mechanism portion of a magnetic recording and reproducing apparatus carrying the rotating head device. That is, the prior art does not take it into account that the overlap between the tape cassette and the rotating head device is hampered by the protrusion of, e. g., the tape cassette lid to be opened for drawing out the tape, and it has had the problem that the reduction of the horizontal area of the mechanism portion of the magnetic recording and reproducing apparatus carrying the rotating head device is impeded.
Meanwhile, in a fixed cylinder device wherein the upper and lower cylinders of a rotating head device are fixed, an air film formed between a tape and the cylinders has heretofore been thin as compared with one in a rotary cylinder system. This is attributed to the absence of the effect of producing the air film as in the conventional rotary cylinder system. In the fixed cylinder device, accordingly, the traveling load of the tape enlarges due to a less or smoothing action based on the air film, and such problems as obstruction to stable traveling and damages to the tape have been prone to occur. These drawbacks have become more conspicuous as the tape thickness has been reduced for a lower rigidity and the tape surface roughened for a higher friction factor and an increase in the density of recording. Developments have therefore been made for forming a sufficient and stable air-smoothing layer also in the fixed cylinder device. An example thereof is as disclosed in the official gazette of Japanese Patent Application Laid-open No. 36361/1984. As shown in FIG. 2 of the drawings annexed herewith, the disclosed device is so constructed that spiral grooves 221 and 222 of the so-called pumping-out type which discharges out air in an internal space are provided between stationary portions including fixed cylinders 201, 202 and a rotating portion 216 including rotating heads, so as to form an air film between a tape and the cylinders. As a result, the contact of the tape with the cylinders is avoided or relieved, and the damage to the tape is eliminated, so that the qualities of recording and reproduction can be enhanced.
In FIG. 2, numeral 214 indicates a rotary shaft, numerals 203 indicate the magnetic heads, and numeral 218 indicates a coil.
The prior art, however, has been problematic in the points of machining and assembling costs for the reasons that the head rotating member needs to be formed with the spiral grooves of complicated shape and that the gaps between the grooves and the fixed cylinders need to be controlled to predetermined narrow intervals. Moreover, since the air is blown out uniformly over the whole outer peripheries of the cylinders, the air layer becomes thicker at the start part of tape winding where the tape exhibits a low tension. As a result, a non-uniform air film is formed, and non-uniformity in the magnetic contact between each rotating head and the tape arises to cause non-uniformity in the physical contact of the two. This has posed the problem that degradation in the contact between the tape and the head, namely, the head-to-tape contact is prone to be incurred.